Microscopic cold crack
A microscopic cold crack is a delayed crack in martensitic structures, triggered by diffusible hydrogen and high residual stresses. It can lead to material damage.
Physical-Chemical Mechanism
Microscopic cold cracks are caused by hydrogen pickup in the metal. This hydrogen is absorbed during welding or by corrosion and can diffuse through the material. Under high residual stresses, as in martensitic microstructures, hydrogen can impair the mechanical strength and lead to microscopic cold cracks.
Metallurgical Relevance & Welding Risks
Microscopic cold cracks can lead to long-term material failure. They are especially dangerous because they appear over time and are hard to detect. This can lead to cracks, fractures, or other mechanical faults in the metal.
Workshop Practice & Action Points
To avoid microscopic cold cracks, keep the material clean and dry before welding. Use suitable protective agents and check the material's watertightness. For heavily loaded or high-stress metal, a post-weld treatment like austenitizing can help remove hydrogen from the material.